The present invention relates to voice coil bobbins for planar diaphragms in planar diaphragm loudspeakers. More particularly, the invention relates to a regular polygonal voice coil bobbin for a corresponding regular polygonal planar diaphragm.
The invention relates to voice coil bobbins for planar diaphragms and more particularly to a voice coil bobbin for a planar diaphragms the weight of which is reduced.
It is known that a planar diaphragm has a relatively flat acoustic pressure characteristic throughout its frequency range thus providing high fidelity sound reproduction. Accordingly, loudspeaker systems employing planar diaphragms have been proposed in the art.
For a collective drive type loudspeaker system using such a planar diaphragm, it is necessary to provide a driver unit capable of subjecting the entire area of the planar diaphragm uniformly to piston motion. Especially, the configuration of a voice coil bobbin coupled directly to the planar diaphragm is of utmost importance. It is desirable that a voice coil bobbin for a regular polygonal planar diaphragm be a corresponding regular polygonal voice coil bobbin having sides arranged parallel to the sides of the regular polygonal planar diaphragm.
A regular polygonal voice coil bobbin, especially a square voice coil bobbin, has a low rigidity at its corners. Accordingly, a square voice coil bobbin cannot be maintained square. That is, the square configuration of the square voice coil bobbin is deformed into a parallelepiped configuration which makes it impossible to uniformly drive the entire area of the diaphragm. In addition, the voice coil bobbin itself should have a considerably high rigidity in order to be able to satisfactorily transmit the driving force generated in the voice coil to the planar diaphragm against the weight of the planar diaphragm.
If the adhesion between a planar diaphragm and its voice coil bobbin is inadequate, then the driving force produced by the voice coil bobbin is not sufficiently transmitted to the diaphragm. Thus, the voice coil bobbin must be positively bonded to the diaphragm. In loudspeakers of this general type, a metal planar diaphragm using a honeycomb core is employed because it is required that the planar diaphragm be light in weight, have a high rigidity and be partially undeformable. Thus, planar diaphragms have been designed to reduce their weight using various techniques. However, the weights of planar diaphragms known to date are still high. In addition to this, the voice coil bobbin coupled to the diaphragm is also relatively heavy. This is undesirable because some of the driving force generated in the voice coil is wasted or ineffectively used.
Planar diaphragm type loudspeaker systems in which bass-range, mid-range and treble-range loudspeakers are mounted on a baffle board are known in the art. One of the advantages of such a planar diaphragm type loudspeaker system is that its acoustic image has very little shift. If a two-way or three-way loudspeaker system mounted on a baffle board is replaced by a corresponding coaxial loudspeaker system, then the amount of shift of the acoustic image is further reduced.
For this purpose, it is desirable to construct a coaxial loudspeaker system in which planar diaphragms are arranged coaxially. However, the assembly of the coaxial loudspeaker system involves problems which do not arise in the construction of ordinary cone type loudspeakers. Specifically, it is rather difficult to connect the voice coils to the feeder wires. That is, although the voice coil of the bass-range diaphragm is positioned near the outermost peripheral portion of the loudspeaker, the voice coils of the mid-range and treble-range diaphragms are positioned near the center of the loudspeaker and therefore it is difficult to introduce the feeder wires into the central portion of the loudspeaker and to lead them out of the central portion.